1. Technical Field
The invention relates to loudspeakers, and in particular, to loudspeakers with split multiple magnets having polarities aligned in the same direction.
2. Related Art
Loudspeakers convert electrical energy into sound and typically include a diaphragm, a magnet structure, and a voice coil. The magnet structure may include one or more magnets and a core cap. The core cap can direct and concentrate a magnetic flux produced by the magnets into a voice coil gap. The voice coil can be connected to the diaphragm and positioned in the voice coil gap. When electrical energy flows into the voice coil, an induced magnetic field can be created that interacts with the magnetic flux in the voice coil gap. The voice coil may carry a current in a direction substantially perpendicular to the direction of the magnetic flux produced by the magnet structure, so that the interaction between the voice coil current and the magnetic flux can cause linear oscillation of the voice coil within the length of the voice coil gap, which moves the diaphragm in order to produce audible sound.
Some loudspeakers utilize a magnet structure including a single relatively thick magnet supported by a magnetically conductive pedestal. This arrangement can allow for clearance suitable for mechanical travel of the voice coil within the voice coil gap to attain the desired amount of magnetic flux to drive the voice coil in the voice coil gap, such as in a subwoofer. However, using a single thick magnet supported by a magnetically conductive pedestal may result in significant fringe magnetic fields that can increase the risk of reducing the efficiency of the loudspeaker. In addition, the voice coil motor force constant (BL) (magnetic flux density (B) multiplied by the effective length (L) of the voice coil wire within the entire length of the air gap) may have asymmetric characteristics. For example, a BL that is non-linear and variable can cause an increased risk of distortion and unsatisfactory performance. Moreover, using a single thick magnet supported by a magnetically conductive pedestal may result in a larger mass loudspeaker which can increase the manufacturing and shipping costs of the loudspeaker. Therefore, a need exists for a loudspeaker magnet structure that can provide reduced fringe magnetic fields. A need also exists for a loudspeaker magnet structure that can provide improved voice coil motor force constant (BL) characteristics, such as linearity, while maintaining a magnetic flux density (B) across the length of the air gap for sufficiently linear voice coil travel and without sacrificing efficiency of the loudspeaker.